Many patients with anginal chest pain, despite angiographically normal coronary arteries, display limitations of coronary blood flow under a variety of conditions. Previous work has established that many of these patients are unable to augment their coronary blood flow normally in response to certain stimuli. They frequently develop chest pain under these conditions in association with both hemodynamic and metabolic evidence for myocardial ischemia. It appears that their reduced ability to increase coronary blood flow in response to stress is a dynamic abnormality of coronary arteries too small to be visualized during angiography. The current protocol was designed to determine the location, extent and severity of such coronary flow abnormalities using Thallium-201 emission computed tomography. Accordingly, 13 patients with previously documented abnormal coronary vasomotor tone underwent Thallium-201 perfusion imaging following an infusion of dipyridamole. Despite the provocation of chest pain and hemodynamic alterations in the majority of these patients, only one patient demonstrated a perfusion defect compatible with regional myocardial ischemia. We have concluded from these studies that dipyridamole Thallium-201 perfusion imaging is an insensitive technique for the visualization and characterization of abnormalities of myocardial blood flow in patients with chest pain and normal coronary arteries. Such negative results may reflect the fact that the regional flow disparities in such patients are of too samll a magnitude to be detected with this current technology.